1. Field of the Invention
The present invention relates to a method of driving an AC (Alternating Current) surface-discharge type plasma display panel that enables a scanning period to be shortened.
The present application claims priority of Japanese Patent Application No. 2001-365650 filed on Nov. 30, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
Currently, two types of plasma display panels are available, one being a DC (Direct Current)-discharge type plasma display panel which is operated by exposing electrodes in a discharge space being filled with a discharging gas and by causing a DC discharge to occur between the exposed electrodes, and another being an AC-discharge type plasma display panel which is operated, with electrodes not directly being exposed in the discharging gas by coating electrodes with dielectric layers, in a state in which AC-discharge occurs. There are two types of the AC-discharge type plasma display panels, one having two electrodes in a display cell and another having three electrodes in the display cell. Configurations and driving methods of a conventional three-electrode-surface-discharge AC-type plasma display panel (hereinafter may be referred simply to as a xe2x80x9cPDPxe2x80x9d) are described below.
FIG. 6 is a perspective view showing configurations of one display cell in the PDP. As shown in FIG. 6, in the display cell, an insulating substrate 1 serving as a rear substrate made of a transparent material such as glass and an insulating substrate 2 serving as a front substrate also made of transparent material such as glass are mounted in parallel to each other. On a surface of the insulating substrate 2 facing the insulating substrate 1 are placed a plurality of transparent scanning electrodes 3 and a plurality of common electrodes 4 alternately at specified intervals. On each of the scanning electrodes 3 and on each of the common electrodes 4 are formed a trace electrode 5 and a trace electrode 6 respectively both serving to reduce an electrode resistance value of each of the scanning electrode 3 and of the common electrodes 4. Moreover, a dielectric film 12 is formed in a manner that it covers the scanning electrodes 3, common electrodes 4, and the trace electrode 5 and electrode 6. On the dielectric film 12 is formed a protective layer 13 made of magnesium oxide or a like which prevents the dielectric film 12 from being affected by discharge.
Moreover, on a surface of the insulating substrate 1 facing the insulating substrate 2 is mounted a plurality of data electrodes 7 each extending in a direction orthogonal to each of the scanning electrodes 3 and the common electrodes 4. On the data electrodes 7 is formed a dielectric film 14 in a manner so as to cover the data electrodes 7.
Between the insulating substrate 1 and the insulating substrate 2 are formed ribs 9 (that is, partitioning walls) used to provide space 8 for discharging gas and to partition a display cell (picture cell). The space 8 for discharging gas is filled with an inert gas such as helium, neon, xenon, or a like or mixed gases of these inert gases. Moreover, on a surface of the dielectric film 14 and on a side of each of the ribs 9 are formed phosphors 11 used to absorb ultraviolet rays produced by discharge of the above gas and to emit visible light 10.
FIG. 7 is a top view schematically showing arrangements of electrodes used in the conventional PDP shown in FIG. 6. As shown in FIG. 7, xe2x80x9cnxe2x80x9d (n is a natural number) pieces of the scanning electrodes 3 (see FIG. 6) (S1 to Sn); xe2x80x9cnxe2x80x9d pieces of the common electrodes 4 (see FIG. 6) (C1 to Cn), and xe2x80x9cmxe2x80x9d (m is a natural number) pieces of the data electrodes 7 (see FIG. 6) (D1 to Dm) are provided in the PDP. Also, as shown in FIG. 7, the PDP is provided with xe2x80x9cnxe2x80x9d pieces of the scanning electrodes S extending in parallel to one another, xe2x80x9cnxe2x80x9d pieces of the common electrodes C extending in parallel to one another, and xe2x80x9cmxe2x80x9d pieces of the data electrodes D extending in a direction orthogonal to the scanning electrodes S and common electrodes C. Display cells 15 are formed, each emitting light and each containing one nearest contact of one of the data electrodes D to one of the scanning electrodes S and one nearest contact of one of the data electrodes D to one of the common electrodes C. That is, one of the scanning electrodes S, one of the common electrodes C, and one of the data electrodes D pass through each of the display cells 15. The display cells 15 are arranged in a matrix form. Therefore, a total number of display cells 15 on an entire screen of the PDP is xe2x80x9c(nxc3x97m)xe2x80x9d.
Next, a method for driving the conventional PDP is described below. FIG. 8 is a timing chart showing periods contained in one field in the method for driving the conventional PDP. The method shown in FIG. 8 is called a xe2x80x9csub-field methodxe2x80x9d. For example, images being switched at a rate of one piece per one sixtieth of a second are displayed in one field 20 which is made up of eight sub-fields SF1 to SF8 and a number of times of sustaining discharge occurring in each sub-field is set to be values each being proportional to a power of two so as to be made different from one another. Here, let it be assumed that the number of times of the sustaining discharge in each of the sub-fields SF1 to SF8 is given by 27k=128k, 26k=64k, 25k=32k, 24k=16k, 23k=8k, 22k=4k, 21k=2k, and 20k=1k, respectively, where xe2x80x9ckxe2x80x9d is a constant coefficient. Then, by arbitrarily selecting sub-fields during which the sustaining discharge occurs, out of these sub-fields SF1 to SF8, and by combining the selected sub-fields, 256 shades of gray are made to be displayed in each of the display cells 15.
FIG. 9 is a diagram showing waveforms of pulses used in the conventional method for driving the PDP for each of the conventional sub-fields (SF1 to SF8). FIGS. 10A to 10C and FIGS. 11A to 11B are diagrams schematically illustrating arrangements of wall charges formed in each of the display cells 15 when the driving method shown in FIG. 9 is executed. FIGS. 10A to 10B are diagrams illustrating arrangements of wall charges formed during a resetting period 21. FIG. 10C is a diagram illustrating arrangements of wall charges formed during a scanning period 22, FIGS. 11A and 11B are diagrams illustrating arrangements of wall charges formed during a sustaining period 23. As shown in FIG. 9, according to the method employed in the above example, each of the sub-fields SF1 to SF8 is divided into the resetting period 21, the scanning period 22, and the sustaining period 23. Hereinafter, operations during each of the above periods the resetting period 21, the scanning period 22, and the sustaining 23 making up the sub-field are explained by referring to FIG. 9, FIGS. 10A to 10C, and FIGS. 11A and 11B. In FIGS. 10A to 10C and FIGS. 11A and 11B, a positive wall charge is expressed by a symbol obtained by enclosing xe2x80x9c+xe2x80x9d with a circle and a negative wall charge is expressed by a symbol obtained by enclosing xe2x80x9cxe2x88x92xe2x80x9d with a circle.
During the resetting period 21, wall charges formed in a previous sub-field (not shown) are erased and displayed data is reset. During the resetting period 21, a priming pulse of a positive polarity Vp+ is applied to each of the scanning electrodes S and, at a same time, a priming pulse of a negative polarity Vpxe2x88x92 is applied to each of the common electrodes C. Each of the data electrodes D is set to be at a ground (GND) potential. A total voltage of the priming pulse of the positive polarity Vp+ and the priming pulse of the negative polarity Vpxe2x88x92 is set to be more than a surface-discharge firing voltage of the conventional PDP. This causes, as illustrated as a state xe2x80x9cA1xe2x80x9d in FIG. 10A, priming discharge (preliminary discharge) to occur between a surface of the dielectric film 12 (see FIG. 6) corresponding to that over the scanning electrodes S (hereinafter may be simply referred to as xe2x80x9cthe surface over the scanning electrode Sxe2x80x9d) and a surface of the dielectric film 12 corresponding to that over the common electrodes C (hereinafter may be simply referred to as xe2x80x9cthe surface over the common electrode Cxe2x80x9d). After the occurrence of the priming discharge, as illustrated as a state xe2x80x9cA2xe2x80x9d in FIG. 10A, negative wall charges are formed (build up) over the specified scanning electrodes S, whereas positive charges are formed (build up) over the specified common electrodes C. After the occurrence of the priming discharge, wall charges are formed in each of the display cells 15 in a manner that a potential being applied to each of the scanning electrodes S and the common electrodes C is countered and, as a result, an electric field in each of the display cells 15 becomes uniform. Therefore, states of the wall charges formed in each of the display cells 15 after the occurrence of the priming discharge becomes the same irrespective of states of wall charges formed in the previous sub-field.
Next, while each of the data electrodes D is kept at a GND potential, a priming erasing pulse Vpe of a negative polarity having a saw-tooth shaped waveform is applied to each of the scanning electrodes S and, at a same time, each of the common electrodes C is made to be at a GND potential. The priming erasing pulse Vpe is a pulse whose potential is lowered continuously from its GND level, which causes a difference in potential to be continuously increased between the surface over the scanning electrodes S and the surface over the common electrodes C and, as a result, as illustrated as the state xe2x80x9cA3xe2x80x9d in FIG. 10B, feeble discharge (priming erasing discharge) occurs between the surface over the scanning electrodes S and the surface over the common electrodes C. Moreover, the feeble discharge represents feeble discharge which continues with a voltage between discharging gaps being kept almost at a discharge firing voltage. This causes, as illustrated as a state xe2x80x9cA4xe2x80x9d in FIG. 10B, wall charges formed by the priming discharge described above (see FIG. 10A) to be erased. As a result, states of wall charges in each of the display cells 15 are reset.
During the scanning period 22, with each of the common electrodes C being kept at a GND potential, a scanning pulse Vw of a negative polarity is applied sequentially to each of the scanning electrodes S1 to Sn. Moreover, during a period of time contained in the scanning period 22 in which the scanning pulse Vw is not applied to each of the scanning electrodes S1 to Sn, a scanning base pulse Vbw of a negative polarity having a constant voltage is applied to each of the scanning electrodes S1 to Sn. The application of the scanning base pulse Vbw to each of the scanning electrodes S1 to Sn causes an amplitude of the scanning pulse Vw to be decreased, which allows a voltage used by a driving IC operated to apply the scanning pulse Vw to be lowered. This can achieve reduction in costs of the PDP production.
Then, a data pulse Vd of a positive polarity is selectively applied, in synchronization with the scanning pulse Vw, to each of the data electrodes D, based on display data. At this point, each of voltages of the scanning pulse Vw and the data pulse Vd is set so as to be individually less than a opposed-discharge firing voltage and is so set that a voltage obtained by superimposing the scanning pulse Vw on the data pulse Vd is not less than the opposed-discharge firing voltage. Moreover, a voltage of the scanning base pulse Vbw is so set that a voltage obtained even by superimposing the scanning base pulse Vbw on the data pulse Vd is less than the opposed-discharge firing voltage.
This enables, as illustrated as a state xe2x80x9cA5xe2x80x9d in FIG. 10C, writing discharge to occur only in a display cell selected out of the display cells 15 based on display data, that is, only in the display cell to which the data pulse Vd is applied in synchronization with the scanning pulse Vw. Here, first, opposed-discharge occurs between over the specified scanning electrodes S and a surface of the dielectric film 14 (see FIG. 6) corresponding to that over the specified data electrodes D (hereinafter may be simply referred to as xe2x80x9cthat over the data electrode Dxe2x80x9d), and then the opposed-discharge triggers surface-discharge to occur between the surface over the scanning electrodes S and the surface over the common electrodes C. A reason why such the surface-discharge occurs is that activated particles such as electrons, atoms, metastable atoms, or like produced in each of the display cells 15 when the above opposed-discharge occurred lower a threshold voltage for the surface-discharge. Discharge obtained by putting the opposed-discharge and surface-discharge together is called xe2x80x9cwriting dischargexe2x80x9d. Moreover, a display cell where writing discharge has occurred is called a xe2x80x9cselected display cellxe2x80x9d and a display cell where the writing discharge has not occurred is called a xe2x80x9cnon-selected display cellxe2x80x9d.
Furthermore, by making the surface over the scanning electrodes S be of a negative polarity when the opposed-discharge making up the writing discharge occurs, bombardment of the protective layer 13 (see FIG. 6) made of MgO (Magnesium Oxide) with a positive ion contained in discharging gas occurs and, as a result, a secondary electron is emitted. The secondary electron is moved to a positive polarity side by an electric field applied to the specified display cells 15 and, as a result, collides with a molecule of the discharging gas, which causes the discharging gas molecule to be ionized to positive ions and electrons. This causes the positive ions and electrons to be further supplied to each of the display cells 15, thus enabling discharge to continuously occur. Moreover, the phosphor 11, when being radiated with ultraviolet rays produced by discharge, emits visible light 10, however, since the ultraviolet rays are not allowed to pass through the MgO layer, the protective layer 13 is preferably formed on a surface of the insulating substrate 2, that is, on the scanning electrodes 3 and common electrodes 4.
As illustrated as a state xe2x80x9cA6xe2x80x9d in FIG. 10C, positive wall charges are formed by the writing discharge on each of the scanning electrodes S and negative wall charges are formed by the writing discharge on each of the common electrodes C and on each of the data electrodes D. The display cell (selected display cell), out of the display cells 15, in which the writing discharge has occurred, serves as a display cell emitting light during the sustaining period 23 described later. Moreover, in the selected display cell, out of the display cells 15, in which the writing discharge has not occurred, states on one of the scanning electrodes S, common electrodes C, and data electrodes D which are arranged within the above display cell remain to be same as illustrated as the state xe2x80x9cA4xe2x80x9d in FIG. 10B, with no wall charges being formed. After the application of the scanning pulse Vw to all the scanning electrodes S has been completed, the scanning period 22 ends and then the sustaining period 23 starts.
During the sustaining period 23, only the display cells 15 selected during the scanning period emit light to perform actual display of images. During the sustaining period 23, each of the data electrodes D is always kept at a GND potential. First, each of the scanning electrodes S is made to be at a GND potential and then a sustaining pulse Vs of a negative polarity is applied to each of the common electrodes C. The sustaining pulse Vs is so set that a difference between a potential of the sustaining pulse Vs and a GND potential is less than a surface-discharge firing voltage and that a voltage of the sustaining pulse Vs exceeds a voltage obtained by subtracting a voltage (wall voltage) induced by the wall charges (see the state xe2x80x9cA6xe2x80x9d in FIG. 10C) formed by the writing discharge described above from the surface-discharge firing voltage. Therefore, in the display cells 15 in which the writing discharge occurred during the scanning period 22, since, as illustrated as the state xe2x80x9cA6xe2x80x9d in FIG. 10C, positive wall charges are formed on each of the scanning electrodes S being arranged within the display cells 15 and negative wall charges are formed on each of the common electrodes C being arranged within the display cells 15, the wall voltage induced by the wall charge is superimposed on the voltage of the sustaining pulse Vs and the resulting voltage exceeds a threshold value for surface-discharge (that is, surface-discharge firing voltage). Thus, as illustrated as a state xe2x80x9cA7xe2x80x9d in FIG. 11A, first-time sustaining discharge occurs between the surface over the scanning electrode S and the surface over the common electrodes C. When the first-time sustaining discharge has occurred, as illustrated as a state xe2x80x9cA8xe2x80x9d in FIG. 11A, negative wall charges are formed on each of the scanning electrodes S being arranged within each of the display cells 15 and positive wall charges are formed on each of the common electrodes C being arranged within each of the display cells 15. Then, as illustrated as a state xe2x80x9cA9xe2x80x9d in FIG. 11B, the sustaining pulse Vs of a negative polarity is applied to each of the scanning electrodes S being arranged in each of the display cells 15 and each of the common electrodes C being arranged in each of the display cells is made to be at a GND potential. This causes, in the display cells 15 in which the first-time sustaining discharge has occurred, the wall charges produced by the first-time sustaining discharge to be superimposed on the voltage of the sustaining pulse Vs applied to each of the scanning electrodes S and the resulting voltage to exceed the surface-discharge firing voltage, which causes a second-time sustaining discharge to occur. As a result, as illustrated as a state xe2x80x9cA10xe2x80x9d in FIG. 11B, positive wall charges are formed on each of the scanning electrodes S and negative wall charges on each of the common electrodes C. Thereafter, similarly as above, a wall voltage induced by wall charges produced by x-th time sustaining discharge is superimposed on a voltage of the sustaining pulse Vs applied (x+1)-th time, which causes (x+1)-th time sustaining discharge to occur.
On the other hand, in non-selected display cells out of the display cells 15 in which the writing discharge has not occurred during the scanning period 22, as illustrated as the state xe2x80x9cA4xe2x80x9d in FIG. 10, since no wall charge is formed, no wall voltage is superimposed on a voltage of the sustaining pulse Vs, thus causing no occurrence of a first-time discharge. Therefore, no sustaining discharge occurs second time and thereafter.
Thus, by repeatedly applying the sustaining pulse, it is possible to have only the display cells 15 selected during the scanning period 22 emit light. Each of the display cells 15 can achieve a desired display of images by selecting sub-fields during which the display cells 15 are to emit light and combining the sub-fields.
However, the conventional technologies described above present following problems as below. That is, when the driving method described above is employed, as the scanning period in one sub-field, time being equivalent to a product of a number of scanning electrodes S (numbers of lines) and writing time (scanning time) is needed and, for example, when a number of lines of the scanning electrodes S is 480 and scanning time per one line is 3 xcexcsec, if one field is made up of eight sub-fields, 11.5 ms is required as total scanning time. The required time of 11.5 ms, when one frame is equivalent to one sixtieths seconds, accounts for about 70% of total time required for driving. That is, the sustaining time during which images are actually displayed accounts for less than 30%.
Recently, it is to be wished that a PDP becomes further higher in definition and can provide increased numbers of shades of gray. However, to make the PDP high definition, a number of scanning lines has to be increased, and to increase the number of shades of gray, a number of sub-fields constituting one field has to be increased and, in either case, an increase in total scanning time is unavoidable. If a ratio of the scanning period to one field increases, a ratio of the sustaining period to one field decreases, which causes luminance of images to be lowered. Therefore, in order to achieve higher definition of the PDP and the increase in the number of shades of gray in the PDP, scanning time per one line has to be shortened, the increase in the ratio of the scanning time to one field has to be inhibited so that a sufficient sustaining period has to be secured.
However, here, a problem arises in that, if scanning time per one line is shortened, a range within which a voltage of the sustaining pulse Vs (hereinafter referred to as a xe2x80x9csustaining voltagexe2x80x9d that enables normal display of images can be set becomes narrow and, in a worst case, a screen flickers. Hereinafter, this problem is described in detail.
FIG. 12 is a graph showing, by plotting a scanning period, that is, scanning time per one line as the abscissa and a sustaining voltage as the ordinate, dependence of a minimum sustaining voltage (Vsmin) required for having sustaining discharge occur in a stable manner and a maximum sustaining voltage (Vsmax) needed to prevent non-selected display cells from emitting light erroneously on a scanning period. Within a range 33 of sustaining voltages encircled by a line showing the minimum sustaining voltage (Vsmin) and a line showing the maximum sustaining voltage (Vsmax) shown in FIG. 12, normal display of images is made possible. Moreover, a size of a panel of the PDP used in measurement in the example is 50 inches. The PDP was driven by the conventional method for driving shown in FIG. 9. As shown in FIG. 12, as the scanning period is more shortened, the minimum sustaining voltage (Vsmin) increases and, at a point where the scanning period is 1 xcexcsec, the minimum sustaining voltage (Vsmin) is larger than the maximum sustaining voltage (Vsmax). That is, if the scanning period is set to be 1 xcexcsec, normal driving of the PDP becomes impossible.
Hereinafter, its reason is explained. FIGS. 13A and 13B are diagrams schematically illustrating behavior in which wall charges are formed after application of a scanning pulse and FIG. 13A shows a case where the scanning period is sufficiently long and FIG. 13B shows a case where the scanning period is short. As shown in FIG. 13A, a certain period of time 31 is needed before a time when light-emitting F occurs since the application of the scanning pulse Vw to each of the scanning electrodes S. Then, when the light-emitting F occurs, discharging gas in each of the display cells 15 is ionized and, as a result, electrons and ions are produced in each of the display cells 15. A period existing after the occurrence of the light-emitting F in the period during which the scanning pulse Vw is being applied to each of the scanning electrodes S is a wall charge attracting period 32. During the wall charge attracting period 32, by an electric field applied within each of the display cells 15, ions produced by the light-emitting F are attracted on each of the scanning electrodes S and electrons produced by the light-emitting F are attracted on each of the common electrodes C and on each of the data electrodes D and, as a result, positive wall charges are formed on each of the scanning electrodes S and negative wall charges are formed on each of the common electrodes C and on each of the data electrodes D.
However, as shown in FIG. 13B, if the scanning period 22, that is, the period during which the scanning pulse Vw is applied to each of the scanning electrodes S is short, the wall charge attracting period 32 becomes short accordingly. As a result, ions and electrons produced in each of the display cells 15 are not attracted sufficiently on each of the scanning electrodes S, the common electrodes C, and the data electrodes D, thus resulting in insufficient formation of the wall charges. Moreover, the electric field produced by the scanning base pulse Vbw being applied to each of the scanning electrodes S after the occurrence of the writing discharge serves to move electrons and ions to each of the scanning electrodes S, the common electrodes C, and the data electrodes D and to induce the formation of wall charges. Therefore, in each of the display cells 15 where the writing discharge occurs in an early stage of the scanning period 22, even if the formation of wall charges induced by the scanning pulse Vw is not sufficient, during the scanning period 22 and thereafter, wall charges are formed, to some extent, by the scanning base pulse Vbw. However, in the display cells 15 in which the writing discharge occurs in a last stage in the scanning period 22, that is, in the display cells 15 existing in a vicinity of a final line to be scanned, if the formation of wall charges induced by the scanning pulse Vw is insufficient, since a period of time during which the scanning base pulse Vbw is applied in the scanning period 22 and thereafter is short, almost no wall charges induced by the scanning base pulse Vbw are formed, as a result, causing the above-described problem to be more serious.
To solve this problem, technology is disclosed in Japanese Patent Application Laid-open No. 2000-206933 in which writing discharge is caused to occur at a high voltage. In this technology, a sub-field is made up of a preliminary discharge period, a scanning period, a converting period, and a sustaining period. Wall charges are formed in a last stage of the preliminary discharge period between the surface over the scanning electrode S and the surface over the data electrodes D. Next, during the scanning period, a data pulse is applied to each of the data electrodes D in a display cell not emitting light and no data pulse is applied to each of the data electrodes D in a display cell emitting light. This causes a relatively large amount of wall charges to occur in the display cell not emitting light and a relatively small amount of wall charges to occur in the display cell emitting light. Then, during the converting period, discharge is made to occur only in the display cell not emitting light to erase the wall charges. As a result, during the sustaining period, sustaining discharge does not occur in the display cell not emitting light and occurs only in the display cell emitting light. Thus, according to this technology, since writing discharge is made to occur at a high voltage, wall charge can be effectively formed after the occurrence of the writing discharge and the scanning time can be shortened accordingly.
However, the technology disclosed in the above Japanese Patent Application Laid-open No. 2000-206933 presents a problem described below. That is, in the driving method employed in the disclosed technology, discharge is made to occur in a display cell not emitting light during the scanning period and the converting period. Therefore, the discharge causes light to be emitted in a display cell in which no discharge occurs, as a result, another problem arises in that luminance (black luminance) increases when a black color is displayed.
In view of the above, it is an object of the present invention to provide a method of driving an AC surface-discharge type plasma display panel capable of shortening a scanning period by securing a wide range in which a voltage to induce sustaining discharge can be set without causing a flicker to occur and black luminance to be increased.
According to a first aspect of the present invention, there is provided a method of driving a surface-discharge alternating current-type plasma display panel having first and second insulating substrates placed so as to face each other, a plurality of scanning electrodes and a plurality of common electrodes being placed on a side of a face of the first insulating substrate facing the second insulating substrate and being extended in a first direction and being alternately arranged, a first dielectric layer to cover the plurality of the scanning electrodes and the plurality of the common electrodes, a plurality of data electrodes being placed on a side of a face of the second insulating substrate facing the first insulating substrate and being extended in a second direction orthogonal to the first direction, and a second dielectric layer to cover the plurality of the data electrodes, for having a surface-discharge alternating-current-type plasma display panel, in which picture cells are formed in a matrix form in a manner that each of the picture cells contains one nearest contact point of one of the plurality of the data electrodes to each of the plurality of the scanning electrodes and one nearest contact point of each of the plurality of the data electrodes to each of the plurality of the common electrodes and that a discharge gap is formed between each of the plurality of the scanning electrodes and each of the plurality of the common electrodes in each of the picture cells, display images based on display data, the method including:
a step of constructing one field to display one image of one sub-field or a plurality of sub-fields and;
wherein the sub-field is made up of a resetting period during which a state of an electric charge in each of the picture cells is initialized, a scanning period during which a scanning pulse is sequentially applied to each of the scanning electrodes and, at a same time, a data pulse is selectively applied, based on the display data, to the data electrodes with same timing as for the scanning pulse to cause writing discharge to selectively occur in each of picture cells, a wall charge forming period during which wall charges are formed in the picture cells where the writing discharge has occurred by application of a wall charge forming pulse having an orientation of an electric field determined by a relative relation of potentials among three types of electrodes one being the scanning electrodes, another being common electrodes, and an other being data electrodes being same as an orientation of an electric field produced at a time of the writing discharge during the scanning period, to one electrode or two or more electrodes selected from a group consisting of the scanning electrodes, the common electrodes, and data electrodes, and a sustaining period during which sustaining discharge is made to occur between a scanning electrode region over the scanning electrode in a surface of the first dielectric layer and a common electrode region over the common electrode in the surface of the first dielectric layer in the picture cell where wall charges have been formed by applying a sustaining pulse alternately to the scanning electrode and the common electrode.
According to a second aspect of the present invention, there is provided a method of driving an AC surface-discharge type plasma display panel having: a first insulating substrate and a second insulating substrate arranged opposite each other, a plurality of scanning electrodes and a plurality of common electrodes alternatively arranged on an opposition surface of the first insulating substrate to the second insulating substrate in a first direction, a plurality of data electrodes arranged on an opposition side of the second insulating substrate to the first insulating substrate in a second direction perpendicular to the first direction, a first dielectric layer formed to cover the plurality of scanning electrodes and the plurality of common electrodes, a second dielectric layer formed to cover the plurality of data electrodes, a plurality of discharge gaps arranged between the scanning electrodes and the common electrodes, and a plurality of picture cells each of which includes one of cross points of the discharge gaps and data electrodes;
a step of constructing one field to display one image of one sub-field or a plurality of sub-fields and;
wherein the sub-field is made up of a resetting period during which a state of an electric charge in each of the picture cells is initialized, a scanning period during which a scanning pulse is sequentially applied to each of the scanning electrodes and, at a same time, a data pulse is selectively applied, based on the display data, to the data electrodes with same timing as for the scanning pulse to cause writing discharge to selectively occur in each of picture cells, a wall charge forming period during which wall charges are formed in the picture cells where the writing discharge has occurred by application of a wall charge forming pulse having an orientation of an electric field determined by a relative relation of potentials among three types of electrodes one being the scanning electrodes, another being common electrodes, and an other being data electrodes being same as an orientation of an electric field produced at a time of the writing discharge during the scanning period, to one electrode or two or more electrodes selected from a group consisting of the scanning electrodes, the common electrodes, and the data electrodes, and a sustaining period during which sustaining discharge is made to occur between a scanning electrode region over the scanning electrode in a surface of the first dielectric layer and a common electrode region over the common electrode in the surface of the first dielectric layer in the picture cell where wall charges have been formed by applying a sustaining pulse alternately to the scanning electrode and the common electrode.
In configurations according to the foregoing first and second aspect, the wall charge forming period is provided between the scanning period and the sustaining period. During the wall charge forming period, by applying the wall charge forming pulse to one electrode or two or more electrodes selected from a group consisting of the scanning electrodes, the common electrodes, and the data electrodes, an electric field being determined by a relative relation in potentials among the three types of electrodes within each of the picture cells is made to occur. An orientation of the electric field is same as that of the electric field produced at the time of writing discharge. Moreover, the orientation of the electric field does not represent a direction of the electric field, that is, represents a polarity of an electric field relative to the electrode and, for example, the electric field existing on a side of each of the scanning electrodes in a picture cell is defined to be of a positive polarity relative to a side of each of the data electrodes and the electric field existing on a side of each of the data electrodes in the picture cell is defined to be of a negative polarity. During the scanning period, discharging gas is ionized by the occurrence of writing discharge in each of the picture cells and ions and electrons are produced in each of the picture cells. By applying the above electric field after the occurrence of the writing discharge, the ions and electrons are attracted on each of the scanning electrodes, the common electrodes, and the data electrodes and wall charges are formed in each of the picture cells. As a result, even if the time interval between the scanning pluses is short and sufficient wall charges can not be formed within application time of the scanning pulse, wall charges can be formed during the wall charge forming period and the sustaining discharge can be made to occur during the sustaining period. This enables scanning pulses to be shortened without causing a flicker on a screen. As a result, the scanning period can be shortened without causing an increase in black luminance and the sustaining period can be secured, thereby enabling improvement of luminance, increases in scanning lines and in the number of shades of gray.
In the foregoing, a preferable mode is one wherein a time interval between the wall charge forming pulses is 3 xcexcsec to 50 xcexcsec.
By making the time interval between the wall charge forming pulses be not less than 3 xcexcsec, a voltage setting range of the sustaining pulse is made wider and a stable driving of the PDP is made easier. On the other hand, by making the time interval between the wall charge forming pulses be less than 50 xcexcsec, saturation of the effects by the wall charge forming pulse can be prevented and, during the wall charge forming period, wall charges can be effectively formed.
Also, a preferable mode is one, wherein, during the scanning period, a scanning pulse of a negative polarity is applied to each of the scanning electrodes and, at a same time, a data pulse of a positive polarity is applied selectively to the desired data electrodes and wherein, during the wall charge forming period, a wall charge forming pulse of a negative polarity is applied to each of the scanning electrodes.
By operating above, during the wall charge forming period, an electric field having almost the same direction as that provided at a time of writing discharge can be applied and positive wall charges can be formed on each of the scanning electrodes and negative wall charges can be formed on each of the common electrodes and the data electrodes.
Also, a preferable mode is one wherein, during the scanning period, a scanning pulse of a negative polarity is applied to each of the scanning electrodes and, at a same time, a data pulse of a positive polarity is selectively applied to the desired data electrodes and wherein, during the wall charge forming period, a wall charge forming pulse of a positive polarity is applied to the common electrodes.
By operating above, positive wall charges can be formed on each of the scanning electrodes and negative wall charges can be formed on each of the common electrodes and, at a same time, a large amount of negative wall charges can be formed on each of the data electrodes. This enables not only surface-discharge but also opposed-discharge to occur in the sustaining discharge and occurrence of the sustaining discharge to be more stable.
Also, a preferable mode is one wherein, during the scanning period, a scanning pulse of a negative polarity is applied to each of the scanning electrodes and, at a same time, a data pulse of a positive polarity is selectively applied to the desired data electrodes and wherein, during the wall charge forming period, a wall charge forming pulse of a negative polarity is applied to each of the scanning electrodes and, at a same time, a wall charge forming pulse of a positive polarity is applied to the desired data electrodes.
Also, a preferable mode is one wherein the wall charge forming pulse of a positive polarity to be applied to the desired data electrodes is obtained by extending time for application of a final data pulse during the scanning period.
By operating above, a driving waveform can be simplified.
Also, a preferable mode is one wherein, during a period of time within the scanning period in which the scanning pulse is not applied to each of the scanning electrodes, a scanning base pulse of a negative polarity whose voltage is less than a voltage obtained by subtracting a voltage of the data pulse from a opposed-discharge firing voltage is applied to each of the scanning electrodes.
By operating above, an amplitude of the scanning pulse can be made smaller and reduction in costs of PDP production can be achieved.
Furthermore, a preferable mode is one wherein the wall charge forming pulse is obtained by extending time for application of the scanning base pulse.
By operating above, a driving waveform can be simplified.
Thus, with the above configurations, an amount of wall charges formed after the occurrence of writing discharge can be increased and a stable shift from a writing period to a sustaining period is made possible. This enables flicker, which occurred in a vicinity of a final line to be scanned due to insufficient formation of wall charges at a time of writing encountered when a scanning period is set to be short as in the conventional technology, to be improved and excellent images to be displayed. As a result, the scanning period can be shortened without causing an increase in black luminance and idle time given by the shortening of the scanning period can be assigned to increase the number of sustaining pulses, sub-fields, and scanning lines. This enables luminance to be enhanced and the number of shades of gray to be increased and image quality to be improved in the PDP.